1. Field of the Invention
The present invention relates to a method of brake lining wear sensing. More specifically, the present invention relates to a method of brake wear sensing based on a temperature versus time history at the lining/shoe interface after application of the brake.
2. Description of the Prior Art
Various brake lining wear detection systems are known in the art. In addition, temperature measurement systems are known, although very few methods are known which combine the capability of detecting brake wear along with detecting the operating temperature of the brake lining. U.S. Pat. No. 5,419,415, the disclosure of which is incorporated herein by reference, discloses an apparatus for monitoring the operating temperature and providing a signal when an elevator brake lining reaches a service wear point. An electrically conductive wire loop and a temperature sensitive resistor are disposed within the brake lining. Monitoring the resistance of the temperature sensitive resistor yields a signal which represents the operating temperature of the brake lining so that extreme temperature conditions can be detected and corrective action taken. Once the electrical conductive loop is worn away, an open circuit is detected which signals the need for lining replacement.
U.S. Pat. No. 4,204,190, the disclosure which is hereby incorporated by reference, describes a brake lining wear detection system where a signal is generated when an embedded conductive wire loop is broken and when electrical contact is made between the wire loop and a brake drum surface thereby indicating the lining wear out point. Likewise, U.S. Pat. No. 3,825,891, the disclosure which is hereby incorporated by reference, describes a brake lining wear sensing system where an electrical circuit signals when an embedded wire loop is broken due to wear of the lining and/or when the wire loop contacts the brake drum. In addition, U.S. Pat. No. 2,494,269, the disclosure which is hereby incorporated by reference, discloses a brake wear and temperature measurement system where a plurality of thermo-responsive elements are disposed within the brake lining where each element is selectively monitored to determine if abnormal temperatures have been encountered and/or whether the brake lining has worn to such an extent that one or more of the thermally responsive elements have been broken.
U.S. Pat. No. 4,646,001, the disclosure of which is incorporated herein by reference, discloses a resistive array connected to a plurality of conductive strips that are embedded within the brake lining. Each wire is located at a selective height of the brake lining and as each conductive strip is broken due to wear of the brake lining, resistive elements are added to the detection circuit, the brake lining wears, the overall resistance of the resistive array increases. The resistive elements themselves are positioned outside of the brake lining to prevent damage and drift due to temperature changes. No temperature sensing capability is included in this particular system.
A more traditional brake temperature indication means is disclosed in U.S. Pat. No. 1,957,051 where a thermocouple is disposed within the brake lining connected to a display means to indicate operating temperature of the brake lining. A similar technique is used in U.S. Pat. No. 4,520,661 where a combination temperature and wear sensor is disposed in a brake cylinder where the sensor has a slider mechanism that is pressed on the face of a brake cylinder to indicate brake wear and also includes a temperature sensing device thereby indicating the wear of the brake lining and overheating of the brake fluid through a pair of lead out wires.
What is needed in the market is a compact, inexpensive and reliable method of measuring brake wear and monitoring brake temperature using one sensor and a processing unit.